1. Field of the Invention
The present invention relates to a throttle valve opening degree detecting system for controlling an internal combustion engine in accordance with the engine speed and degree of throttle valve opening.
2. Description of Related Art
The degree of throttle valve opening which is an essential parameter to control the engine, and can be obtained with a throttle sensor. Various types of throttle sensors have been proposed heretofore. However, none of conventional throttle sensors have a sufficient resolution for a range of small degrees of throttle valve opening.
In particular, in engine control systems, the degree of throttle valve opening becomes an important source of information for detecting the operation load of an engine. A throttle sensor for detecting the degree of opening is generally constructed of a rheostat, such as disclosed in Japanese Utility Model Laid-open Publication Nos. 57-92107 and 59-66106. An output voltage proportional to the degree of throttle valve opening can be obtained from the sensor. This output voltage undergoes analog/digital conversion by a control unit and is supplied to a computer.
However, there are problems associated with conventional throttle sensors. Namely, the degree of throttle valve opening is not proportional to the engine load (e.g., pressure within the intake pipe) so that the engine load is non-linear relative to the degree of throttle valve opening as shown in FIG. 5. More specifically, for low engine speeds, the engine load sharply changes for small degrees of throttle valve opening, and less for large degrees of throttle valve opening. As a result, it becomes necessary to detect the degree of throttle valve opening with a high resolution for low engine speeds and small degrees of throttle valve opening, in order to precisely control the engine. However, the above-mentioned conventional throttle sensor cannot obtain a sufficient resolution engine control for low engine speeds and small degrees of throttle valve opening.